Part 1. A quick review. Then: The “stars” of cell activity– ENZYMES

 Everything the body needs (food, water, oxygen) and does (physical movements, thinking) comes down to the needs each cell to conduct its business in coordination with other cells of the organ within which it resides. Consider muscle cells needing to contract, nerve cells conducting impulses, cells of salivary glands secreting digestive enzymes, and so on.

From countless exacting studies and examination of photographs taken with the electron microscope, each cell is revealed to be a highly complex structure with numerous sub-cellular components as illustrated in the following link. 

https://www.istockphoto.com/vector/animal-cell-structure-gm1155003177-314285683?phrase=human%20cell%20diagram

Bring discussion to the conclusion: to maintain life, each cell must be continually regenerating and repairing its parts in addition to performing whatever specialized task it is performing for the body as a whole. 

How does a cell perform its tasks? 

The multitude of tasks come down to 1000s of distinct chemical reactions that result in the synthesize of necessary products, or cause particular actions, e.g., contraction of a muscle fiber, to occur. In short, hundreds of chemical reactions are going on simultaneously and continuously in each and every cell.

Have students visualize: If all the necessary chemicals were put in a jar and shaken, it would be rare, if ever, for a proper reaction to occur. 

The cell’s secret is ENZYMES: each cell makes 100s of specific enzymes, one particular kind enzyme for each chemical reaction that is to occur.

A given enzyme catalyzes a single specific chemical reaction. To catalyze means the reaction is made precise—the same reactants yield exactly the same products, plus, the reaction is speeded up 1000s to millions-fold. Further the enzyme itself is not changed by the reaction; it can perform the same operation on molecule after molecule.   

The following video is an animation of a particular enzyme performing a specific chemical reaction. You may ignore the technical words regarding the chemical involved. Note just the high points:

1. The enzyme is a large complex protein molecule (to be described shortly in Part 2.)
2. The reactant(s) bind to the enzyme and are held in a precise position to enable a specific reaction (change in the reactant molecule) to occur  
3. the product(s) are released leaving the enzyme unchanged so that it can conduct the same reaction repeatedly.
4. Again, there is a separate and distinct enzyme molecule for each of the 1000s of unique chemical reactions that occur in each cell of the whole body.

Both the general picture and the action of a particular enzyme (one of the many 100s) is depicted in the following video.